Slag-forming agent for steelmaking

ABSTRACT

A method of making steel comprising adding to molten steel a slag-forming agent comprising from 2 to 20% by weight of metallic titanium particles having a size of 0.5 to 20 mm., 30 to 94% by weight of aluminum oxide, and a binder.

United States Patent [1 1 Takashima 1 May 13,1975

1 1 SLAG-FORMING AGENT FOR STEELMAKING [75] Inventor: Masaru Takashima,Tokyo, Japan [73] Assignee: Aikoh Co. Ltd., Tokyo, Japan [22] Filed:Sept. 27, 1973 [21] Appl. No.: 401,269

Related U.S. Application Data [63] Continuation-in-part of Ser. No.225,286, Feb. 10,

1972, abandoned.

[30] Foreign Application Priority Data [56] References Cited UNITEDSTATES PATENTS 1,002,133 8/1911 Bryant et a1. 75/93 A 1,331,816 2/1920McKnight, .lr. 164/56 2,748,040 5/1956 Conn 148/26 3,214,806 11/1965 Foxet a1 75/96 X 3,234,608 2/1966 Peras 164/56 X 3,414,042 12/1968 Behrenset al. 164/57 3,731,868 5/1973 Arikawa et al. 75/94 X FOREIGN PATENTS ORAPPLICATIONS 570,480 2/1959 Canada 164/57 Primary Examiner--Allen B.Curtis Assistant ExaminerThomas A. Waltz Attorney, Agent, or Firm-D.Paul Weaver [57] ABSTRACT A method of making steel comprising adding tomolten steel a slag-forming agent comprising from 2 to 20% by weight ofmetallic titanium particles having a size of 0.5 to 20 mm., 30 to 94% byweight of aluminum oxide, and a binder.

7 Claims, No Drawings 1 SLAG-FORMING AGENT FOR STEELMAKING BACKGROUND OFTHE INVENTION This application is a continuation-in-part of Ser. No.225,286 filed Feb. 10, 1972, now abandoned.

The present invention relates to a method of making steel using aslag-forming agent which is added to the steel in the furnace.

Limestone, fluorspar, scrap of silica brick, or a mixture thereof havebeen conventionally used as a slagforming agent in making steel in aconverter, an electric furnace, or an open hearth furnace. Fluorspar hasbeen the preferred slag-forming agent is steelmaking because it improvesthe fluidity of the slag and is economical. However, fluorspar (CaF is afluoride, and generates fluorine gas during the steelmaking processwhich damages the walls of the furnace and obstructs the workingenvironment. Although fluorspar ideally should contain more than 85% byweight of CaF when used in steelmaking, many available fluorspars areshort in CaF content and so are not as desirable for use in steelmaking.

It has been discovered that aluminum ash consisting of mainly aluminumoxide and containing metallic aluminum deoxidizes the slag insteelmaking. For example, the aluminum ash reduces chromium oxide in theslag of chromium alloy steel to metallic chromium, thereby adding morechromium to the molten steel to increase the amount of chromium in themolten steel. This in turn reduces the amount of fluorspar needed, andaccelerates the speed of slag-formation and shortens the reducing time.

However, the metallic aluminum ash in the molten steel, even if it is afine powder, remains in the molten steel as aluminum oxide, which has adeleterious effect on the molten steel. At the same time, when it isused in continuous casting of molten steel, the aluminum oxide presentin the molten steel adheres to and clogs the nozzle of the tundish, andmakes casting impossible by combining with manganese oxide or silicondioxide. Additionally, aluminum is very reactive with oxygen and isinstantaneously oxidized at the high temperature inside the furnace sothat the amount of aluminum available as a deoxidizing agent is only30-50% of that added to the melt. This makes aluminum very expen- 'siveas a slag-forming agent, as well as very inefficient.

SUMMARY OF THE INVENTION The object of the present invention is toprovide a process for making steel which does not have the disadvantagesof methods using the above-described slag forming agents.

According to the present invention, steel is made by incorporating intothe molten steel a slag-forming agent containing metallic titanium aswell as aluminum oxide. This slag-forming agent deoxidizes molten steel,and the resulting titanium oxide floats easily on the molten steel sothat it can be readily removed therefrom. Therefore, even in thecontinuous casting of molten steel, the titanium dioxide does not clogthe nozzle of the tundish. As metallic titanium does not react withoxygen as readily as aluminum does, it is not oxidized instantaneously,and almost all of the metallic titanium is available as an oxidizingagent for a long time. The

method of the present invention accelerates the speed of slag-forming,reduces the amount of fluorspar used,

and results in an improved dephosphorizing and desulfurizing rate ascompared with prior art methods.

The slag-forming agent for use in the method according to the presentinvention comprises from 2 to 20% by weight of metallic titaniumparticles having a size of 0.5 to 20 mm., 30 to 94% by weight ofaluminum oxide, and 4 to 20% by weight of a binder.

As metallic titanium or titanium alloy containing in excess of by weightof titanium metal is expensive, it is most economical to use scraps.Less than 2% by weight of titanium in the slag-forming agent isineffective, and more than 20% by weight to titanium does not give agreater effect than 20%. The size of the metallic titanium particles islimited to 0.5 mm. to 20 mm. to enhance the speed of the reaction. Thetitanium is more easily oxidized and thus is less effective at particlesizes below 0.5 mm., and the reaction is too slow when the particle sizeexceeds 20 mm.

Although alumina brick powder, bauxite, aluminum ash or aluminum drossare a preferable material for supplying aluminum oxide in theslag-forming agent of the present invention, other alumina containingmaterials can be also used. The aluminum ash is a slag which is formedwhen metallic aluminum is refined and the aluminum dross is a floatingslag which is formed when metallic aluminum is remelted. Although thealuminum ash or dross has a defect in that its composition is notuniform, these materials, which contain as a main component aluminumoxide and also contain some metallic aluminum, are formed from the slagwhich is developed when metallic aluminum is refined or remelted andoxides are formed from the flux. Therefore, these materials areeconomically beneficial and preferable.

Also, it is desirable to use various kinds of synthetic resin binders,organic binders such as animal or vegetable glue, starch and dextrin, orinorganic binders such as various kinds of cement, water glass andbentonite to make the slag-forming agent according to the presentinvention, into a molding of a 10-50 mm. briquette, tablet or pellet bya roll pressing machine or a granulating tablet-making machine. Theorganic binder is preferably used in a quantity of 4 to 12% by weightand the inorganic binder is preferably used in a quantity of 7 to 20% byweight.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention isillustrated by the following examples.

Examples using the slag-forming agent according to the present inventionare shown in Table l in comparison with the prior slag-forming agent.

(A1 0 content: 60%) (Metallic aluminum: 24%) 3 TABLE l-ContinuedSlag-Forming Agent of the Present lnvention Material A B C Bauxite 27 72(Alcontent:

Titanium and Its Alloys Titanium metal (Size: 2-6 mm.) (Purity: 99.3%)Titanium alloy (Size: -20 mm.) (Titanium content:

Binder.

Self-hardening phenol resin (Solid component of 60% methanol solution)Portland cement Size of Molding (mm.) (Briquette) method.

could not be done. However, in the case of Nos. 1, 2 and 3, when theslag-forming agents (A, B, and C), containing metallic titaniumaccording to the present invention, were used, smooth casting waspossible without clogging the nozzle. Also, by adding smaller amount ofthe slag-forming agents (A, B and C) according to the present inventioncompared to the conventional slag-forming agent, the yield of chromiumadded, as shown in Table 2, was improved and the reduction time could beshortened because of the rapid rate in which the slag was formed.

Test 2 Each of the slag-forming agents (A, B and C) according to thepresent invention and the conventional slagforming agent (D) having thesame composition and size (Table l) and fluorspar were charged togetherwith scrap at the time of making common steel by a 100 ton converteroperation, and blowing was done by an ordinary operation. The resultsare shown in Table 3. Nos. 1 and 2 are the results when only fluorsparwas used. Nos. 3 and 4 are the results when the conventionalslag-forming agent (D) was used, and Nos. 5 through 10 are the resultswhen the slag-forming agents (A, B and C) relating to the presentinvention were used.

As shown in Table 3, by using about 1 kilogram per ton of theslag-forming agents (A, B and C) according to the present invention,-theamount of fluorspar used could be decreased by approximately 3 kilogramsper ton compared to the time when only fluorspar (Nos. 1 and 2) wasused, and the amount of fluorspar used could be slightly decreasedcompared to the time when conventional slag-forming agent (D) (Nos. 3and 4) was used. Further, the dephosphorizing rate and the desulfurizingrate could be improved and the steelmaking time could be shortenedbecause of the rapid rate at TABLE 3 Comparative Table on the Results ofUsing Slag-Fonning Agent Amount used of limestone (kg/t) 60.4 60.5 60.260.5 60.3 59,8 60.3 60.5 60.2 60.5 Amount of fluorspar (kg/t) Chargingin advance 3.0 3.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Chargin later 2.4 2.51.0 0.8 0.4 0.3 0.2 0.2 0.2 0.2 Amount 0 slag-forming agent A 1.0 1.0according to the present B 1.0 1.0 invention (kg/t)* C 1.0 1.0 Amount ofconventional slag- D 1.2 1.3 forming agent (kg/t)* Dephosphorizing rate89.3 88.6 89.5 90.4 90.8 90.5 92.3 91.8 91.3 90.8 Desulfurizing rate35.2 35.4 34.6 36.3 38.1 38.8 40.1 39.5 38.6 39.1

*Charging in advance.

TABLE 2 which the slag-forming agent according to the present inventionforms the slag. Therefore, the slag-forming Comparative Table on theResults agent according to the present invention was found to of UsingSlag-Forming Agent be desirable.

No 2 N03 No 4 As described above, by making steel using a slagslagpm.ming Agent forming agent containing metallic titanium, there is noAdded danger of titanium dioxide remaining in the molten 3 8:3 2 5 Isteel. In the case of continuous casting, there is no clogc (kg) ging ofthe nozzle of the tundish and deoxidation of the 1) (kg) 230 Yield ofChromium 98.3% 97.8% 98.9% 91.6% Slag example the f of steel made Addedaccording to the present invention 15 higher than the In the case of No.4, when the conventional slagforming agent (D) was used, the nozzle ofthe tundish was clogged during continuous casting and casting chromiumcontent of steel made acccording to the 5 prior art process.Additionally, the steelmaking time per charge is reduced because of therapid rate at which slag is formed as compared with the prior artprocess. Thus, efficiency of the steelmaking process is improved.Further, the amount of fluorspar necessary can be decreased and thedesulfurization and dephosphorization rates can be improved.

What is claimed is:

1. A method for making steel comprising adding to molten steel aslag-forming agent comprising 2 to by weight of metallic titaniumparticles, to 94% by weight of aluminum oxide, and 4 to 20% by weight ofa binder.

2. The method of claim 1 wherein the metallic tita nium particles rangefrom 0.5 mm. to 20 mm.

3. The method of claim 1 wherein the metallic titanium particles are inthe form of titanium alloy containing at least 80% by weight of metallictitanium.

group consisting of a briquette, a tablet, and a pellet. =l

1. A METHOD FOR MAKING STEEL COMPRISING ADDING TO MOLTEN STEEL ASLAG-FORMING AGENT COMPRISING 2 TO 20% BY WEIGHT OF METALLIC TITANIUMPARTICLES, 30 TO 94% BY WEIGHT OF ALUMINUM OXIDE, AND 4 TO 20% BY WEIGHTOF A BINDER.
 2. The method of claim 1 wherein the metallic titaniumparticles range from 0.5 mm. to 20 mm.
 3. The method of claim 1 whereinthe metallic titanium particles are in the form of titanium alloycontaining at least 80% by weight of metallic titanium.
 4. The method ofclaim 1 wherein the aluminum oxide is selected from the group consistingof alumina brick powder, bauxite powder, aluminum ash, and aluminumdross.
 5. The method of claim 1 wherein the binder is selected from thegroup consisting of synthetic resin, animal glue, vegetable glue, starchand dextrin.
 6. The method of claim 1 wherein the binder is selectedfrom the group consisting of cement, water glass, and bentonite.
 7. Themethod of claim 1 wherein the slag-forming agent is in the form of amolding selected from the group consisting of a briquette, a tablet, anda pellet.